Systems Engineering Modelling Diagrams as Prerequisites to Failure Mode and Effect Analysis

Failure mode and effect analysis (FMEA) process starts with several key inputs. A few such traditional inputs are the older generation FMEAs, field failure reports, corrective actions and lessons learned. During the past two decades there had been several diagrams used as important FMEA inputs. The most popular diagrams of all diagrams had been the boundary diagram and the parameter diagram that were used to discover hidden functional requirements and failure modes for Design FMEAs. Similarly, the Process Flow Diagram had been used to discover process steps as input to Process FMEAs. This paper discusses several other diagrams depending on the stage of the product development process. FMEAs begin with Functional Requirements. The two main issues affecting the effectiveness of DFMEA are the (i) poorly written functional requirements and (ii) the missing functional requirements. The main connection and the contribution of this paper to DFMEA is the discovery process of functional requirements, otherwise missed. Once the functional requirements are discovered, the rest of the elements of FMEAs are derived from those functional requirements. For example, failure modes are derived as over-function, underfunction, or no function, etc. Therefore, missed and poorly written requirements are going to affect the effectiveness of the all elements of FMEA, thereby the product designed level for reliability. The requirements come from different sources. They could be performance, regulatory, safety, or environmental, to mention a few. As mentioned before, if requirements are missed in a FMEA, verification and validation of that requirement is going to be missed. In addition, poorly written requirements lead to inadequate verification and validation test plans. The traditional Boundary and Parameter Diagrams have been influential as a multidimensional tool in discovering the initial requirements. To strengthen the multidimensional requirement discovery process, systems engineering modeling language (SysML) offers several other diagrams. Few examples are the activity diagrams, sequence diagrams, state machines diagrams and use case diagrams. This paper discusses such popular and useful SysML diagrams used across new product development processes to discover functional requirements that may be missed otherwise and feed the DFMEA to have a good start to an effective FMEAs. Examples are provided from automobile, wind turbine, and heating & air-conditioning industries.